Field of the Disclosure
The present disclosure relates to a substrate for a display device, and more particularly, to a substrate including a photosensitive organic insulating layer and a method of fabricating the substrate.
Discussion of the Related Art
In general, a liquid crystal display (LCD) device may be driven based on optical anisotropy and polarization of liquid crystals (LCs). Since LC molecules are thin and long, the LC molecules may be arranged in a specific direction, and the direction in which the LC molecules are arranged may be controlled by artificially applying an electric field to the LCs.
That is, when the arrangement of the LC molecules is changed using the electric field, light may be refracted due to the optical anisotropy of the LCs in the direction in which the LC molecules are arranged, so that images can be displayed.
In recent years, an active-matrix LCD (AM-LCD) device in which TFTs and pixel electrodes are arranged in matrix shapes has attracted much attention because the device has a high resolution and is highly capable of embodying moving images.
The LCD device includes an array substrate having a pixel electrode, a color filter substrate having a common electrode and a liquid crystal layer interposed between the array substrate and the color filter substrate. The array substrate includes a plurality of pixel regions and a thin film transistor (TFT) is formed in each pixel region. The pixel electrode is connected to the TFT through a contact hole of an insulating layer.
The contact hole may be formed through a photolithographic process including a step of coating a photoresist (PR), a step of forming a PR pattern by exposure and development, and a step of etching an insulating layer using the PR pattern as an etching mask.
A process where a step of coating the PR and a step of etching the insulating layer are omitted by forming the insulating layer between the TFT and the pixel electrode using a photosensitive organic material such as a photo acryl has been researched.
The photosensitive organic material including the PR and the photo acryl may be classified into a positive type and a negative type according to a dissolution property in a developer after exposure. A solubility of an exposed portion of a positive type photosensitive organic material increases so that the exposed portion can be removed after development, while a solubility of an exposed portion of a negative type photosensitive organic material decreases so that an unexposed portion can be removed after development.
The photosensitive organic material is exposed to an ultraviolet (UV) ray emitted from a mercury (Hg) lamp. For example, the photosensitive organic material may be cured by the i-line UV ray of an having a wavelength of about 365 nm. When a pattern of a photo mask has a relatively large size (critical dimension: CD), an influence of diffraction is relatively small so that an influence of a diffracted light can be minimized. However, when a pattern of a photo mask has a relatively small size, a shape of a pattern of the photosensitive organic material may be distorted by the diffracted light.
Specifically, a size of a contact hole in an insulating layer is reduced to improve aperture ratio and brightness of a display device. Deterioration of a fine contact hole due to the diffracted light becomes a serious problem.